This invention relates to airbag inflators and systems utilizing same for enhancement of driver and passenger protection, including side impact protection, in motor vehicles and the like.
Conventional airbag inflators have relatively complex structures with elements such as forged housings defining internal ignition, combustion, and filter chambers by integrally formed and/or welded internal partitions. Furthermore, coolant structures, such as filters formed from heat conductive materials and the like, in many cases require the foregoing structural complexities in order to withstand the temperatures and pressures generated within these inflator structures.
Many of such conventional inflators use azide based gas generating materials such as sodium azide based materials which have relatively high burn rates and undesirable toxicity levels and products of combustion such as mists and ash associated therewith.
Accordingly, there is a need in the prior art for more simplistic inflator structures, such as those formed from sheet metal having internal chambers formed in part by improved coolant/filter structures and utilizing non-azide propellants having controllable burn rates, gas volume production, internal pressures, and internal temperatures to increase the effectiveness of airbag inflators while reducing the size and the cost thereof and producing lesser amounts of undesirable products of combustion such as mists and ash.
The azide-based gas generating material (NaN3/CuO, for example) has a relatively high linear burning velocity of about 45-50 mm/sec under the pressure of 70 kg/cm2. Because of the relatively high linear burning velocity, the azide-based gas generating material, even in the form of relatively large pellets or disk-shaped pieces with an excellent shape retention capability, can satisfy the required complete combustion time of 40-60 msec when used, for example, in the airbag inflator for the airbag at the driver""s seat side.
Non-azide gas generating materials, which have been developed, are excellent in terms of impacts on environment and safety of passengers. Such materials, however, have the linear burning velocity of less than 30 mm/sec in general. If it is assumed that the linear burning velocity is about 20 mm/sec and that the gas generating material is manufactured in the form of pellets of 2 mm in diameter or disks of 2 mm thick, which are advantageous in retaining their shapes, the combustion speed will be about 100 mm/sec, which fails to meet the desired combustion time of 40-60 msec. When the linear burning velocity is approximately 20 mm/sec, to obtain the desired combustion time requires that the material""s pellet diameter or disk thickness to be about 1 mm. When the linear burning velocity is less than 10 mm/sec, the gas generating material""s disk is required to have a thickness of 0.5 mm or less. Thus, it is practically impossible to manufacture the gas generating material in the form of pellets or disks that are industrially stable and can withstand many hours of vibrations of an automobile. It has been difficult to develop the airbag inflator that meets the desired performances.
By way of specific example, reference is made to FIG. 9 wherein a conventional airbag inflator such as disclosed in U.S. Pat. No. 4,547,342 of Adams et al., Oct. 15, 1985 is shown.
A housing 40 has a diffuser shell 41 and a closure shell 42. The diffuser shell 41 is formed by forging and has three concentric cylinders 43, 44, 45 formed integral with a circular portion 46. Like the diffuser shell 41, the closure shell 42 is also formed by forging and has three concentric welded portions 50, 51, 52. The diffuser shell 41 and the closure shell 42 are joined together at these welded portions 50, 51, 52 by friction welding. It is common in the prior art to form the shells of the airbag inflator by forging.
In this airbag inflator, the cylinder 43 defines an ignition means accommodating chamber 53, the cylinder 44 defines a combustion chamber 54, and the cylinder 45 defines a coolant/filter chamber 55. The ignition means accommodating chamber 53 accommodates ignition means comprising an igniter 56 and a transfer charge 47. In the combustion chamber 54, pellets of a gas generating material 57, ignited by the ignition means to produce a gas, and a first coolant/filter 58 surrounding the gas generating material 57 to cool the combustion gas and arrest combustion particulates are installed. In the coolant/filter chamber 55, a second coolant/filter 59 to further cool the combustion gas and arrest combustion particulates is installed.
Forged products, though they are homogeneous in the metal structure and highly tenacious, have a drawback of high cost. When the shell members having many concentric cylinders as disclosed in the above U.S. patent are manufactured by forging, the circular portion 46 is not flat and requires a cutting work, which increases the number of manufacturing processes and therefore increasing cost. In the shell member having the cylinder 43 formed integral with the circular portion 46 as in the above U.S. patent, when the volume of the cylinder 43 is to be changed, the overall shape of the diffuser shell 41 needs to be changed. Changing the volume of the cylinder 43, therefore, is not easy. In the above conventional airbag inflator, because the coolant/filter chamber is formed outside the combustion chamber, the diameter of the airbag inflator becomes large, increasing its size and weight. Further, because the combustion chamber is defined by the cylinder 44 of the diffuser shell, the diffuser shell is complex in shape, making the manufacture of the airbag inflator difficult, thus increasing the cost.
As a further example, a coolant for an airbag inflator is obtained by rolling a strip-like metal mesh into a multi-layer cylinder. The coolant cools a combustion gas generated in the combustion chamber of the airbag inflator as it passes therethrough and entraps relatively large combustion particulates. FIG. 12 illustrates an airbag inflator equipped with a conventional coolant similar to that shown in U.S. Pat. No. 4,902,036 to Zander et al., issued Feb. 20, 1990. The airbag inflator comprises a housing 231 having gas discharge ports 230, an ignition means accommodating chamber 232 defined at a central portion in the housing 231, a combustion chamber 233 defined on the outer side of the ignition means accommodating chamber 232, and a coolant/filter chamber 234 defined on the outer side of the combustion chamber 233. In the ignition means accommodating chamber 232, ignition means or an igniter 235 and a transfer charge 236 are disposed, and in the combustion chamber 233, a canister 238 filled with a gas generating material 237 which is ignited by the ignition means and generates a gas is disposed, and in the coolant/filter chamber 234, a coolant 239 for cooling the combustion gas generated in the combustion chamber 233 and a filter 240 for cleaning the combustion gas are disposed. The combustion chamber 233 is defined by a cup-like combustor cup 243, having ports 244 for releasing the combustion gas, and a center hole 245 formed in the bottom thereof. The coolant/filter chamber 234 is divided by a retainer 242 into an upper chamber and a lower chamber. The upper chamber contains a filter 240 and the lower chamber contains a coolant 239.
When a sensor (not shown) detects an impact, a signal is sent to the igniter 235, which is then actuated to ignite the transfer charge 236 to produce flame of a high temperature and high pressure. The flame passes through an opening 241, breaks through the wall of the canister 238 and ignites the gas generating material 237 contained therein. Thus, the gas generating material 237 burns to generate a gas which gushes through the ports 244 formed in the combustor cup 243 and the gas is cooled as it passes through the coolant 239. Here, relatively large combustion particulates are entrapped and the remaining combustion particulates are entrapped as the gas further passes through the filter 240. The gas, that is cooled and cleaned, is discharged through the gas discharge ports 230 and flows into an airbag (not shown). Thus, the airbag inflates to form a cushion between a passenger and a hard structure to protect the passenger from the impact.
The conventional coolant still has a problem from the standpoint of effectively entrapping fine combustion particulates because of its simple clearance structure. Therefore, a filter must be used in addition to the coolant. Moreover, the conventional coolant has a small pressure loss (has a good gas permeability), which makes it difficult to define a pressure chamber such as combustion chamber. It is, therefore, necessary to form a combustion chamber separately from the coolant by using a defining member such as a combustor cup, combustion ring, etc.
Therefore, the airbag inflator, equipped with the conventional coolant, uses an increased number of parts, and has an increased diameter resulting in an increase in the size and weight.
Furthermore, the conventional coolant, having a small bulk density (a value obtained by dividing a mass of the molded article by a bulk volume thereof), is not capable of defining a pressure chamber, has a small shape-retaining strength and, hence, deformed upon the application of a gas pressure, adversely affecting the entrapping of combustion particulates.
It is an object of the present invention to provide an improved and relatively simplistic airbag inflator structure.
Another object of the present invention is to provide an improved airbag inflator structure utilizing a coolant/filter structure that defines an outer peripheral boundary of a combustion chamber within the inflator containing a gas generating material.
Another object of the present invention is to provide an improved and simplistic airbag inflator structure that utilizes non-azide gas generating materials.
Still another object of the present invention is to provide an improved and simplistic airbag inflator structure that uses non-azide gas generating materials and improved coolant/filter structures that defines an outer periphery of a combustion chamber within said inflator containing said non-azide gas generating materials.
Still another object of the present invention is to provide an improved and simplistic airbag inflator structure that incorporates an improved cooperation between the outer housing of the structure and an internal coolant/filter structure defining an outer periphery of a combustion chamber internal to said outer housing.
Yet another object of the present invention is to provide airbag inflator structures and systems for driver, passenger, and side impact applications that utilizes the structures, components, and/or propellants of the present invention.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawings which are directed to several preferred embodiments, components, and propellants forming a part of and/or associated with the inflators of the present invention.
A. The Overall Structure:
The airbag inflator of this invention comprises: a housing having a diffuser shell and a closure shell, the diffuser shell being formed by pressing a metal plate and having gas discharge ports, the closure shell being formed by pressing a metal plate and having a center hole; a central cylinder member made of a pipe, installed in the housing, and disposed concentric with the center hole to form an ignition means accommodating chamber; and a coolant/filter disposed surrounding the central cylinder member to define a combustion chamber for a gas generating means and having a pressure loss of 0.3xc3x9710xe2x88x922 to 1.5xc3x9710xe2x88x922 kg/cm2 at a flow rate of 100 l/min/cm2 at a normal temperature, the coolant/filter being adapted to cool a combustion gas and arrest combustion particulates; wherein a gas generated in the combustion chamber when an impact occurs is introduced into an airbag to protect a passenger from the impact.
One preferred embodiment of the airbag inflator of this invention thus includes a diffuser shell, a closure shell, a central cylinder member, and a coolant/filter. These four members are manufactured separately. That is, the diffuser shell and the closure shell are formed by pressing a metal plate; the central cylinder member is made, preferably, by rolling a metal plate into a cylinder and welding its opposing sides; and the coolant/filter is made, preferably, by stacking flat plaited metal meshes in a radial direction and compressing them in radial and axial directions.
By separating, from the diffuser shell, the central cylinder member that has been formed integral with the circular portion of the diffuser shell in the prior art, the shape of the diffuser shell is simplified. Because of this separated forming, the volume of the central cylinder member can be changed, as required, independently of the diffuser shell. The central cylinder member can be manufactured at low cost by using, for example, the UO press method. Such a welded pipe can be made by the UO press method (which involves the steps of forming a plate in a U shape, then forming it into an O shape, and welding the seam) or an electro-resistance-welding method (which involves the steps of rolling a plate into a cylinder and passing a large current while applying a pressure at the seam to weld the seam by resistance heat).
Forming the diffuser shell and the closure shell by pressing makes their manufacture easy and reduces their manufacture cost.
The coolant/filter of the airbag inflator is arranged surrounding the central cylinder member to define, together with the housing, a combustion chamber for a gas generating means. Further, because of its relatively large, predetermined pressure loss, the coolant/filter of the airbag inflator of this invention can arrest combustion contaminants or particulates contained in the combustion gas with high efficiency. Hence, the filter that has conventionally been provided in addition to a coolant can be obviated.
An alternative embodiment of the inflator structure eliminates the central cylinder by use of an ignition canister centrally located in the housing and mounted on the closure shell within the combustion chamber defined by the coolant/filter and the housing. The coolant/filter is referred to herein as a coolant/filter structure or device to better describe its duality of function in cooling and filtering gas generated by the preferably non-azide gas generating material.
In one preferred embodiment, the pressure loss through the coolant/filter structure is preferably set at 0.5xc3x9710xe2x88x922 to 1.2xc3x9710xe2x88x922 kg/cm2 at the flow rate of 100 l/min/cm2 at normal temperatures. More preferably, it is set at 0.7xc3x9710xe2x88x922 to 0.9xc3x9710xe2x88x922 kg/cm2 at the flow rate of 100 l/min/cm2 at normal temperatures. In the case where an additional mesh layer is provided to strengthen the coolant/filter, that layer has a pressure loss of at least 1.5xc3x9710xe2x88x922 kg/cm2 under these same conditions.
A suitable solid gas generating means for the airbag inflator includes pellets of a gas generating material of NQ/Sr(NO3)2/CMC. This is a mixture of 32.4% NQ (nitroguanidine) by weight, 57.6% Sr(NO3)2 (strontium nitrate) by weight, and 10% CMC (carboxymethyl-cellulose) by weight. NQ functions as a fuel, Sr(NO3)2 as an oxidizing agent, and CMC as a binder.
The solid gas generating material preferably has a linear burning velocity of 5-30 mm/sec under the pressure of 70 kg/cm2 and more preferably 5-15 mm/sec.
The diffuser shell and the closure shell are made of a stainless steel plate 1.2 to 3.0 mm thick. The diffuser shell has the outer diameter of 45 to 75 mm and the closure shell 45 to 75 mm. It is preferred that a narrow space of 1.0 to 4.0 mm wide be formed between an outer circumferential wall formed by the diffuser shell and closure shell and the coolant/filter.
The diffuser shell and the closure shell together form the housing of the airbag inflator, and at least one of the shells may be formed with a mounting flange. The diffuser shell and the closure shell can be joined together by a variety of welding methods, such as plasma welding, friction welding, projection welding, electron beam welding, laser welding, and TIG arc welding. As to the material of the diffuser shell and the closure shell, a nickel-plated steel plate may be used instead of the stainless steel plate. The narrow space between the outer circumferential wall formed by the diffuser shell and closure shell has a role as a gas passage, through which the gas cooled and cleaned by the coolant/filter passes to reach the gas discharge ports of the diffuser shell.
The gas discharge ports of the diffuser shell may have a diameter of 2.0 to 5.0 mm and a total of 12 to 24 such ports may be arranged in the circumferential direction.
The central cylinder member for an electrically activated inflator is formed of a pipe, which is made by rolling a stainless steel plate having 1.2 to 3.0 mm thick into a cylinder 17 to 22 mm in outer diameter and welding the opposing sides. In the case of a mechanically-actuated inflator, the central cylinder plate is 1.5 to 7.5 mm thick with an outside diameter of 19 to 30 mm.
The central cylinder member preferably has a total of six to nine through-holes 1.5 to 3.0 mm across arranged in the circumferential direction. These through-holes are arranged in two staggered rows, one of which may consist, for example, of three through-holes 1.5 mm in diameter and the other may consist of three through-holes 2.5 mm in diameter. The central cylinder member forms a hollow chamber for accommodating ignition means comprising an igniter and a transfer charge. The through-holes allow flames of the transfer charge to be ejected therethrough. The central cylinder member has its inner circumferential portion tapped with a female thread and the igniter is formed with a male thread at its outer circumferential portion. By screwing the igniter into the central cylinder member, the ignition means can be securely fixed in the central cylinder member. Alternatively, the central cylinder member may have a swaged portion at one end, which is swaged to fix the ignition means to the central cylinder member. It can also be secured by welding. The method of fixing the central cylinder member to the diffuser shell includes friction welding, projection welding, laser welding, arc welding, and electron beam welding.
The coolant/filter is preferably made by stacking the flat-plaited metal meshes in the radial direction and then compressing them in the radial and axial directions. The coolant/filter thus formed has a complex clearance structure and thus an excellent arresting capability. In this way, an integrated coolant/filter having both the cooling function and the arresting function is realized. In a preferred embodiment, such a coolant/filter has a pressure loss of 0.3xc3x9710xe2x88x922 to 1.5xc3x9710xe2x88x922 kg/cm2 under the conditions of a normal temperature and a flow rate of 100 l/min/cm2.
In more concrete terms, the steps of making the coolant/filter involves forming a flat-plaited stainless steel mesh into a cylinder, repetitively folding one end portion of the cylinder outwardly to form an annular multi-layer body, and compressing the multi-layer body in a die. Alternatively, the coolant/filter may be made by forming a flat-plaited stainless steel mesh into a cylinder, pressing the cylinder in the radial direction to form a plate member, rolling the plate member into a multi-layer cylinder body, and compressing the multi-layer cylinder body in a die. The stainless steels that are used for the meshes include SUS304, SUS310S, and SUS316 (JIS Standard). SUS304 (18Cr-8Ni-0.06C), an austenite stainless steel, exhibits an excellent corrosion resistance.
The coolant/filter may also be formed in a double layer structure having a mesh with a wire diameter of 0.3 to 0.5 mm and, on the inner side of the mesh, a layer 1.5 to 2.0 mm thick of a mesh with a wire diameter of 0.5 to 0.6 mm. The inner mesh layer has a coolant/filter protection function, i.e., protecting the coolant/filter against the flames from the ignition material ejected toward the coolant/filter and against the combustion gas produced when the gas generating material is ignited and burned by the flames.
The coolant/filter may have an outer diameter of 55 to 65 mm, an inner diameter of 45 to 55 mm and a height of 26 to 32 mm, namely, a thickness of the filter is 5 to 10 mm. Alternatively, the outer diameter may be 40 to 65 mm, the inner diameter 30 to 55 mm and the height 19 to 37.6 mm. The coolant/filter preferably has a coolant/filter support member for blocking its displacement. The coolant/filter support member has a flame resisting portion that is disposed facing the flame through-holes formed in the central cylinder member and covers the inner circumferential surface of the coolant/filter. The flame resisting portion has a coolant/filter protection function to protect the coolant/filter from the flames ejected toward the coolant/filter, and a combustion facilitating function to change the direction of flame propagation to ensure that the flames from the ignition material reach the entire gas generating material. The coolant/filter support member may be formed of a stainless steel plate or steel plate of 0.5 to 1.0 mm thick.
To prevent entry of external moisture into the housing, the gas discharge ports of the diffuser shell are preferably closed with an aluminum sealing tape having a width of 2 to 3.5 times the diameter of the gas discharge ports. Sticking of the aluminum tape can be achieved by using, for example, adhesive aluminum tapes or bonding agents and, more preferably, hot melt adhesives that are melted by heat and can offer secure bonding.
A cushion for the gas generating material can be installed in the combustion chamber. The cushion is made of a stainless steel mesh and secured to an inner surface of the closure shell. The support plate preferably has bent portions at its inner and outer circumferential portions, whose elasticity securely positions the support plate between the central cylinder member and the coolant/filter. When the cushion is formed of a stainless steel mesh, it can also serve as a coolant. The cushion can also be formed of a silicon foam body.
The overall height of the housing is preferably in the range of between 30 and 35 mm.
The coolant/filter has a predetermined wire diameter and a predetermined bulk density. The proper setting of the wire diameter and the bulk density also make it possible to arrest combustion particulates of the burning gas well and increase the shape retaining strength of the coolant/filter significantly, thus preventing the coolant/filter from being deformed by the gas pressure, assuring the normal function of arresting combustion contaminant particulates and allowing the coolant/filter to be reduced in thickness. This bulk density is preferably from 3.5 to 4.5 g/cm3, but may be from 3.0 to 5.0 g/cm3 with a wire diameter of 0.3 to 0.6 mm.
Instead of a metal mesh, a sintered metal may be used to form the coolant/filter device. The coolant/filter can also be made from a composite material of metal and ceramics or from a foamed metal body.
Several other embodiments of the coolant/filter structure are provided and will be more fully described in the detailed description of the invention in connection with the accompanying drawings.
The present invention also can be utilized in an aluminum housing such that as disclosed in U.S. Pat. No. 5,466,420. In this case, the housing, having a thickness of 2-4 mm, is formed by means other than press forming, and the diffuser shell is connected to the closure shell by friction welding.
The airbag inflator apparatus of the present invention comprises:
an airbag inflator including:
a housing having a diffuser shell and a closure shell, the diffuser shell being formed by pressing a metal plate and having gas discharge ports, the closure shell being formed by pressing a metal plate and having a center hole;
a central cylinder member made of a pipe, installed in the housing, and disposed concentric with the center hole to form an ignition means accommodating chamber; and
a coolant/filter made of a metal mesh with a wire diameter of 0.3 to 0.6 mm, having a bulk density of 3.0 to 5.0 g/cm3, disposed surrounding the central cylinder member to define a combustion chamber for a gas generating means and having a pressure loss of 0.3xc3x9710xe2x88x922 to 1.5xc3x9710xe2x88x922 kg/cm2 at a flow rate of 100 l/min/cm2 at a normal temperature, the coolant/filter being adapted to cool a combustion gas and arrest combustion particulates;
an impact sensor for detecting an impact and outputting an impact detection signal;
a control unit for receiving the impact detection signal and outputting a drive signal to the ignition means of the airbag inflator;
an airbag to be inflated by admitting a gas generated by the airbag inflator; and
a module case for accommodating the airbag.
B. Short Pass Prevention
Another embodiment of the invention provides the ability to form the inflator housing of relatively thin stock by preventing gases from distorting the housing and by-passing the end faces of the coolant/filter as a result of this distortion. The present invention provides a combined coolant/filter and cooperative baffle structure precluding such a short pass or bypass of the coolant/filter, as will be more fully described in the detailed description of the drawings. Without such preventative structure, unfiltered combustion particulates can exit the inflator and damage the associated airbag. The structures provided are for both driver, passenger, and side impact inflator configurations.
C. Housing Parameters Accommodating Non-azide Propellants
In order to accommodate the relatively slow burning velocities (less than 30 mm/sec) of many non-azide propellants, and to insure complete combustion of the gas generating materials in the proper time intervals for driver, passenger, and side impact applications, a ratio A/At, where A is the total surface area of the gas generating material and At is the total area of the gas discharge or gas diffuser ports in the diffuser shell of the inflator housing is adjusted.
In the case of a driver-side airbag inflator, the preferred amount of non-azide propellant is on the order of 20 to 50 g. For passenger-side applications, the preferred amount of non-azide propellant is 40 to 120 g; and for side impact applications, 10 to 25 g. This combustion parameter is further enhanced by controlling the particulate size of the non-azide gas generating material as will be more fully described herein. Other parameters, that are controlled, are the internal volume of the inflator housing and the quantity of gas generating material, also to be more fully described herein.
Further optimization of gas flow is achieved by controlling the radial (annular) cross-sectional area St of the defined gas passage or gap between the coolant/filter and the housing end walls to be equal to or greater than the total area At of the gas discharge or diffuser ports. It is preferred that this ratio St/At should preferably fall in the range of 1 to 10 and more preferably 2 to 5.
In order to maintain this annular cross-sectional area of the gas passage or gap, the coolant/filter is provided with an external perforated cylindrical reinforcement defining the inner wall of the gas passage and preventing expansion of the coolant/filter into that passage under the pressure of the generated gas. Other suitable external peripheral supporting layers may also be provided for this purpose.
Coolant/filter structures of the present invention control the solid particulate content of expelled gas from the diffuser ports to less than 2 g and preferably from less than 1 g to less than 0.7 g.
Furthermore, the total area At of the diffuser ports/volume of gas produced is maintained above a desired index and the area At controlled by the size and number of the diffuser ports such that a maximum pressure range of 100 to 300 kg/cm2 is maintained within an inflator housing having a volume of 130 cc or less, for non-azide gas generating materials whose linear combustion velocity 30 mm/sec or less under a pressure of 70 kg/cm2. At a housing volume of 120 cc, the total area of the gas discharge ports is preferably 1.13 cm2.